Wheel suspensions including leaf springs are common for heavy-duty vehicles, especially for vehicles built on a frame made of longitudinal beams. Two or more leaf springs are as a rule mounted in the form of a leaf spring assembly attached at its ends to the underside of the frame. In order to allow a resilient movement of an axle mounted in the center of the assembly, one end of the assembly can be movably mounted relative to the frame, the leaf springs being displaceable in the longitudinal direction.
A conventional wheel suspension of this kind requires two attachment points on the frame. This contributes to problems with the packing of other components and equipment which have to be mounted on and around the frame. The problem is especially great in connection with front-wheel suspensions, where components for suspension and steering have to be adapted to the space for the engine. The problems are correspondingly greater for vehicles with twin front axles where two leaf spring assemblies carry a bogie suspension with two axles. For vehicles with bogie suspension, problems of variation in the toe-in of the front wheels can arise on account of different stiffness in the spring assemblies. As a rule, a conventional wheel suspension with leaf springs also requires support by reaction struts and link arms. Each such component added to the wheel suspension increases the weight of the vehicle.
The conventional solution with an axle mounted in the center of a leaf spring assembly can also give rise to further problems. An example of this is the tendency of the wheel bearing housing to be rotated during braking of the vehicle, something that is known as wind-up stiffness, with an attendant change in camber.